Objectives and methods
We measured soil respiration for two growing seasons to investigate differences
in Jeffers Brook (most fertile), Hubbard Brook (intermediate), and Bartlett (C6
and C9, least fertile) in the White Mountains of New Hampshire. At each site, we
had one mature stand (~100 years post-harvest) and one young stand (~30 years
post-harvest).

Soil respiration was measured every three to four weeks during
summer (June – August) and every four to five weeks during spring (March - May)
and fall (September – November) in 2009 and
2010 using an IRGA system (LI-8100). Five PVC
collars were permanently inserted 1 to 4 cm into the soil in each plot (20
collars per site). Soil respiration measurements were made between 10:00 AM and
2:00 PM.

Results
Soil respiration was higher in old stands than young stands (by 2 – 17%; p
= 0.11-0.34) (Figure 1). Soil respiration was highest in stands where soil
nutrients were lowest (Figure 1). Annual soil respiration was highest at
Bartlett, (1103 g C/m2/yr in the old stand), intermediate at Hubbard Brook, and
lowest at Jeffers Brook, (669 g C/m2/yr in the young stand) (p = 0.06)
(Figure 2). These results support that forests allocate more carbon belowground
in ecosystems with low nutrient availability. Also, these results suggest that
old stands have higher soil respiration than young stands.

Figure
1. Observed soil respiration in young and old in Bartlett (BEF), Hubbard Brook (HB),
and Jeffer’s Brook (JB). Bars are standard error of the mean (n = 20 measurement
points per stand). Bottom graphs are separated by site.